This invention relates to the general area of mechanical microwave switches, often referred to as "coaxial switches" or "coaxial relays".
Microwave switches are designed to accommodate signals ranging in frequency from 0 Hz (i.e., d.c.) to above 40 GHz. Unlike general purpose mechanical switches and relays, microwave switches must maintain an essentially constant impedance over a broad range of frequencies so that the signal characteristics are not affected by the switch.
There are three generally recognized, critical requirements for microwave switches. First, there should ideally be no losses of the signal passing through the switch when the switch is closed. A measure for specifying the losses is defined as "Insertion Loss", and is usually expressed in dB as a function of frequency. Second, no signal should pass through the switch, ideally, when the switch is open. A measure for quantifying this characteristic is called "Isolation" and is also typically expressed in dB as a function of frequency. Third, the parameter quantifying the quality of maintaining a constant characteristic impedance as a function of frequency is usually referred to as "Return Loss" and is also typically stated in dB.
Of the three parameters identified above, the provision of an optimal "Isolation" characteristic is particularly difficult at microwave frequencies. The reason for the difficulty is that even the smallest amount of capacitance between the open switch contacts will quickly deteriorate the isolation between the input and output terminals as frequency increases.